1. Field of the Invention
The present invention relates to a catalyst filling method in a micro channel and a reforming apparatus manufactured by the method. More particularly, the invention relates to a catalyst filling method in a micro channel, which fills the catalyst for reforming fuel in a microchannel more effectively, uniformly and densely using water and gravity, thereby obtaining a highly efficient reforming effect and achieving miniaturization of a fuel cell, and to a reforming apparatus manufactured by the method.
2. Description of the Related Art
Recently, there have been increased uses of portable small-sized electronic devices including mobile phones, Personal Digital Assistants (PDAs), digital cameras, notebook computers and the like. In particular, since the launch of Digital Multimedia Broadcasting (DMB) through the mobile phones, the portable small-sized terminals are required to have increased power capacity. Lithium ion secondary batteries used in general to date, which have capacity for two-hour viewing of DMB, are undergoing efforts to improve their capacity, but there have been growing expectations on small-sized fuel cells for a more fundamental solution.
In order to realize such a small-sized fuel cell, either direct methanol type in which methanol is directly supplied to a fuel electrode or reformed hydrogen fuel cell (RHFC) type in which hydrogen is extracted from methanol and supplied to a fuel electrode can be adopted. The RHFC type uses hydrogen as fuel as in Polymer Electrode Membrane (PEM) type, thus having advantages in terms of output, power capacity per volume and in that it requires no reactants besides water. However, the method requires a reformer, thus having a disadvantage for miniaturization.
In order for the fuel cell system to achieve high power output density, a reformer is required to convert liquid fuel into gaseous fuel such as hydrogen gas. The reformer includes an evaporating part for gasifying methanol and a reforming part for converting methanol into hydrogen via catalytic reaction at a temperature ranging from 250° C. to 290° C.
In the reforming part, heat absorption reaction takes place and the temperature should be maintained from 250° C. to 290° C.
As a conventional example, Japanese Patent Application Publication No. 2003-048701 discloses are forming apparatus 350 as shown in FIG. 1. As shown in FIG. 1, such a conventional micro reforming apparatus 350 has an inner cavity 354 in an evaporating chamber 352 and a heater 356 disposed in the cavity 354 for evaporating fuel. The cavity 354 has a fuel spray 358 installed therein to spray a mixed liquid 360 of methyl alcohol and water, which is the fuel. The sprayed mixed liquid fuel 360 is heated and evaporated by the heater 356.
The gas produced by gasifying the mixed liquid 360 flows through a micro channel 362 and is reformed into hydrogen and carbon dioxide by a reforming catalyst 364 formed in the micro channel 362. In such a reformer 350, reforming catalyst 364 is coated inside the micro-channel 362.
FIG. 2 illustrates the process of coating the reforming catalysts inside the micro channel of the above-described reforming apparatus.
The most representative way of implementing such a process is dip coating, which entails as shown in FIG. 2(a) forming Ta—Si—O—N to form a thin film heater 402 and sputtering Au to form an electrode layer 404, sequentially on a silicon wafer 400.
In addition, as shown in FIG. 2(b), patterns are formed on the thin film heater 402 and the electrode layer 404, respectively, by photolithography. Then, an insulation film 406 is formed as shown in FIG. 2(c), and a photoresist is formed on an opposite side of the silicon wafer 400 by photolithography.
In addition, as shown in FIG. 2(d), channels 410 are formed by sand blasting in an undersurface of the silicon wafer 400, and the silicon wafer 400 is diced into several pieces as shown in FIG. 2(e).
Then, as shown in FIG. 2(f), a Cu/ZnO/Al2O3 catalyst layer 412 is coated in the channel 410. In this step, in order for a selective catalyst coating in the channel 410, a dry film photoresist 414 is applied on portions of the wafer excluding the portions of the channel 410. Then, using dip coating, an Al2O3 Boehmite layer 411 is formed in the channel. This is to increase the adhesive strength between the catalyst and the wall of the channel.
Then, the Al2O3 Boehmite layer 411 is dried at 100° C. and then the Cu/ZnO/Al2O3 catalyst layer 412 is formed as shown in FIG. 2(g) by dip coating. After the coating is completed, the resultant structure is anodic-bonded with a pyrex glass substrate 420 to complete a reformer 440 as shown in FIG. 2(h).
However, the conventional reforming apparatuses 350 and 440 have inefficiency in the process of reforming the fuel gas. That is, the fuel gas is reformed as it passes through the channels 362 and 410 of the reforming apparatus, but in the conventional reforming apparatuses 350 and 440, the fuel gas reacts with limited areas of the catalyst layers 364 and 412, thus lowering the conversion rate of the fuel gas into hydrogen.